1. Field of the Invention
The invention relates to a method of manufacturing a device whereby in a photolithographic treatment subsequently at least two partial masks are aligned relative to the same substrate and a photoresist layer is illuminated through these partial masks in order to obtain connected images having an overlapping connection region, a first illumination through a first partial mask at the connection region forming first halves of details in the photoresist layer with increasing scales of grey towards their ends (decreasing illumination), and a second illumination through a second partial mask forming second halves of the details in the photoresist layer corresponding to the first halves with increasing scales of grey (decreasing illumination) towards their ends, which overlap the ends mentioned above, these scales of grey being complimentary to the scales of grey formed during the first illumination, so that in total a complete illumination of the details is obtained by the two illuminations.
The overlapping connection area is thus formed by ends of halves of details imaged in the photoresist layer.
2. Description of the Related Art
A method of the kind described in the opening paragraph is known from J. P. Rominger "Seamless Stitching for Large Area Integrated Circuit Manufacturing" Optical/Laser Microlithography, Burn J. Lin, Editor, proc. SPIE, 922, pp. 188-14 193 (1988).
Increasingly small details are required in the manufacture of integrated semiconductor circuits, for which imaging systems with high resolution are used, the so-called wafer steppers.
The imaging field of a stepper, however, is limited in size. Since increasingly large surface areas are required for the integrated circuits, it can happen that a semiconductor device no longer fits the imaging field. If such a device is to be manufactured nevertheless, the mask may be split up into various partial masks and the partial masks may subsequently be imaged on a slice of semiconductor material.
In order to let corresponding details of the circuit merge fluently into one another in the case of illumination through subsequent partial masks, the ends of details of adjoining images are given complementary scales of grey at the area of their connection region.
The publication mentioned above describes how the scales of grey are obtained by giving the mask used an extra mask which is not in the object plane of the imaging system, so that half-shadow is obtained in the image plane.
This last-mentioned manufacturing method has a number of disadvantages:
1. Extra process steps are required for manufacturing the masks. PA1 2. In the case of imaging systems which are not telecentric, the position of the half-shadow in the image plane relative to the connection region depends on the distance between the connection region and the optical axis of the imaging system. PA1 3. Corresponding ends of partial masks must end on a straight connection line. This limits the possibilities for circuit design. A connection line is a line which connects and divides into two the ends of adjoining details in a partial mask and which runs practically parallel to the nearby edge of the partial mask in these ends. PA1 4. Connections between ends of partial masks which run parallel to a connection line are not very well possible. PA1 5. A very wide connection region is required between adjoining images, i.e. in the order of 150-1000 .mu.m.